1. Field of the Invention
The invention relates to a power steering system for a motor vehicle and to a method of influencing the damping of a power steering system.
2. Description of Related Art
Power steering systems providing to the driver a steering assist force in steering maneuvers are generally known from the prior art. Regarding the damping behavior of a power steering system, it has turned out to be of advantage to damp any steering forces applied actively by the driver out of a center position of the steering wheel only slightly or not at all and, on the other hand, to provide stronger damping of an automatic return motion of the steering wheel into its center position (when the driver has largely released the steering wheel). Since, owing to the weak or absent damping, the steering behavior is very direct, the driver's own steering movements give him/her a secure steering feel. When the driver releases the steering wheel for an automatic return motion into the center position of the steering wheel, however, a strong damping of external impulses such as, e.g., bumps in the road will occur. This improves on the return motion properties of the steering system and on vehicle safety in general.
DE 39 29 176 C2, and corresponding U.S. Pat. No. 5,072,804 A1, both of which are incorporated by reference herein, already describes a power steering system in which different damping values may be provided depending on the direction of actuation of the steering wheel. The term direction of actuation of the steering system here means, for one thing, the cramping of the wheels, i.e. from driving straight ahead to driving around a bend, and, for the other, the returning of the wheels from driving around a bend to driving straight ahead. The input quantities used here are the angular velocity of the steering wheel and the steering torque, which are then converted into an appropriately adjusted damping moment in a complex process.
It is an object of the present invention to simplify the method of influencing the damping of a power steering system and to provide a power steering system which, depending on the respective steering situation, provides different damping moments involving little expense.